Polymer-coated blade with abrasive tip

ABSTRACT

A friction interface in a gas turbine engine includes an abradable component, such as a seal, and an abrasive component, such as a blade tip, in rubbing contact with each other. The abradable component is composed of a polymer matrix composite and the abrasive component is composed of a metal matrix with hard particles dispersed through the metal matrix. The metal matrix is an aluminum alloy and the hard particles are selected from oxides, nitrides, carbides, oxycarbides, oxynitrides, diamond and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure is a continuation of U.S. patent application Ser.No. 14/592,933 filed Jan. 9, 2015, which claims priority to U.S.Provisional Application No. 61/939923, filed Feb. 14, 2014.

BACKGROUND

This disclosure relates to abrasive tips for rotatable blades. Abradableseals or coatings (rub coatings) can be used to protect moving partsfrom damage during rub interaction while providing a small clearance.Such seals are used in turbomachines to interface with abrasive tips ofa rotating blade stage.

SUMMARY

A friction interface in a gas turbine engine according to an example ofthe present disclosure includes an abradable component and an abrasivecomponent in rubbing contact with each other. The abradable component iscomposed of a polymer matrix composite and the abrasive component iscomposed of a metal matrix and hard particles dispersed through themetal matrix, and the metal matrix is an aluminum alloy and the hardparticles are selected from the group consisting of oxides, nitrides,carbides, oxycarbides, oxynitrides, diamond and combinations thereof.

In a further embodiment of any of the foregoing embodiments, thealuminum alloy is a eutectic aluminum-silicon alloy.

In a further embodiment of any of the foregoing embodiments, the hardparticles have a particle size of 10 micrometers to 200 micrometers.

In a further embodiment of any of the foregoing embodiments, the hardparticles protrude from the metal matrix.

In a further embodiment of any of the foregoing embodiments, theabrasive component has, by volume percent, 0.1% to 50% of the hardparticles.

In a further embodiment of any of the foregoing embodiments, theabrasive component has 5% to 15% of the hard particles.

In a further embodiment of any of the foregoing embodiments, the polymermatrix composite includes a silica-containing filler.

In a further embodiment of any of the foregoing embodiments, thesilica-containing filler is hollow glass microspheres.

In a further embodiment of any of the foregoing embodiments, the hardparticles include at least one of alumina or zirconia.

In a further embodiment of any of the foregoing embodiments, theabrasive component has, by volume percent, 5% to 15% of the hardparticles.

In a further embodiment of any of the foregoing embodiments, thealuminum alloy is a eutectic aluminum-silicon alloy.

A friction interface in a gas turbine engine according to an example ofthe present disclosure includes an abradable seal and an abrasive tip inrubbing contact with each other. The abradable seal is composed of apolymer matrix composite and the abrasive tip is composed of a metalmatrix and hard particles dispersed through the metal matrix, and themetal matrix is aluminum alloy and the hard particles are selected fromthe group consisting of oxides, nitrides, carbides, oxycarbides,oxynitrides, diamond and combinations thereof.

In a further embodiment of any of the foregoing embodiments, the polymermatrix composite includes a silica-containing filler.

In a further embodiment of any of the foregoing embodiments, thesilica-containing filler is hollow glass microspheres.

In a further embodiment of any of the foregoing embodiments, the hardparticles include at least one of alumina or zirconia.

In a further embodiment of any of the foregoing embodiments, theabrasive component has, by volume percent, 5% to 15% of the hardparticles.

In a further embodiment of any of the foregoing embodiments, thealuminum alloy is a eutectic aluminum-silicon alloy.

A blade according to an example of the present disclosure include anairfoil section extending between leading and trailing edges, first andsecond opposed sides each joining the leading and trailing edges, and aninner end and a free tip end. The airfoil section is formed of ametal-based material with a polymeric overcoat on at least one of theleading edge, trailing edge, first side and second side. The airfoilsection includes an abrasive tip at the free tip end. The abrasive tipincludes a metal matrix and hard particles dispersed through the metalmatrix, and the metal matrix is composed of an aluminum alloy and thehard particles are selected from the group consisting of oxides,nitrides, carbides, oxycarbides, oxynitrides, diamond and combinationsthereof.

In a further embodiment of any of the foregoing embodiments, the polymermatrix composite includes hollow glass microspheres.

In a further embodiment of any of the foregoing embodiments, thealuminum alloy is a eutectic aluminum-silicon alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example gas turbine engine.

FIG. 2 illustrates an isolated view of the fan section of the gasturbine engine of FIG. 1.

FIG. 3 illustrates an abrasive tip interfacing with an abradable seal.

FIG. 4 illustrates a cross-section of an abrasive tip.

FIG. 5 illustrates a cross-section of another example in which ametallic bond coat bonds an abrasive tip to an airfoil section.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a fan case 15, and into a core flow path C tothe compressor section 24 for compression and communication into thecombustor section 26 then expansion through the turbine section 28.Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five (5:1). Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption” (TSFC)—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that operating point. “low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7 °R)]^(0.5). The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

FIG. 2 illustrates an isolated view of the fan section 22 of the engine20. The fan 42 includes a rotor 60 that has a plurality ofcircumferentially-spaced blades 62. Each blade 62 includes an airfoilsection 64 that extends between leading and trailing edges 66/68, firstand second opposed sides 70/72 that each joins the leading and trailingedges 66/68, and an inner end 74 and a free tip end 76. Each bladeincludes an abrasive tip 78 at the free tip end 76.

The fan case 15 is annular in shape and circumscribes the blades 62. Thefan section 22 is designed such that the abrasive tips 78 of the blades62 rub against the fan case 15 during rotation. In this regard, the fancase 15 includes an abradable seal 80 mounted on a radially inner sideof the fan case 15. The abradable seal 80 is formed of a polymeric-basedmaterial, such as a polymer matrix composite. In one further example,the polymer matrix composite includes an epoxy matrix and asilica-containing filler dispersed through the matrix. In a furtherexample, the silica-containing filler is or includes hollow glassmicrospheres. An example is 3M™ Scotch-Weld™ Structural Void FillingCompound EC-3555.

When two components are in rubbing contact, at least one of thecomponents may wear. The term “abradable” refers to the one of the twocomponents that wears, while the other component is “abrasive” and doesnot wear or wears less. Thus, when the abrasive tips 78 of the blades 62rub against the seal 80, the seal 80 will be worn whereas the abrasivetips 78 will not wear or will wear less than the seal 80. The word“abrasive” thus also implies that there is or can be contact with anabradable component.

FIG. 3 shows a cutaway view of a representative portion of the airfoilsection 64 of one of the blades 62 and a portion of the abradable seal80. The airfoil section 64 is formed of a metal-based material with apolymeric overcoat 62 a on the surfaces thereof. For example, thepolymeric overcoat 62 a serves to protect the underlying airfoil section64 from erosion due to foreign particulate ingested into the engine 20.In one example, the metal-based material of the airfoil section 64 is analuminum alloy.

The polymeric coating 62 a can be a polyurethane-based coating, anepoxy-based coating, or a silicone rubber-based coating, but is notlimited to these types of polymeric coatings or materials. The polymericcoating 62 a can cover the first and second sides 70/72 of the blades 62and can span the entire lateral surface of the blade 62 between theleading and trailing edges 66/68.

Friction between a blade tip and a surrounding case generates heat. Theheat can be conducted into the case, into the blade, or both. However,in particular for metal blades and polymeric-based cases, the metal ofthe blade is generally a better thermal conductor than the polymer ofthe case, and a majority of the heat thus can conduct into the blade.While this may normally not present any detriments for a plain metalblade, the heat conduction can be detrimental to a metal blade that hasa polymeric overcoat because the heat can cause delamination of thepolymeric overcoat and thus compromise the erosion protection. In thisregard, the abrasive tip 78 has a composition selected with respect toheat-induced delamination of the polymeric overcoat 62 a from frictionalheat generated during rubbing between the abrasive tip 78 and theabradable seal 80. That is, the respective compositions of the abradableseal 80 and the abrasive tip 78 are complimentarily selected withrespect to frictional heat generated and heat-induced delamination ofthe polymeric overcoat 62 a. For example, the compositions are selectedwith regard to a blade temperature at which the polymeric overcoat 62 adoes not delaminate or has a defined delamination durability over anextended period of time, such as the life of the engine 20.

FIG. 4 illustrates a cross-section of representative portion of afurther example of the abrasive tip 78. In this example, the abrasivetip 78 includes a metal matrix 90 and hard particles 92 dispersedthrough the metal matrix 90. In one further example, the metal matrix 90and the metal-based material of the airfoil section 64 arecompositionally composed of the same predominant metal, which canpromote strong adhesion if the abrasive tip 78 interfaces with themetal-based material (i.e., the abrasive tip 78 is in direct contactwith the metal-based material, as depicted in FIG. 4). As an example,the metal can be aluminum.

In one further example, the metal matrix 90 is a eutecticaluminum-silicon alloy having a composition, by atomic weight, of 88%aluminum and 12% silicon. The eutectic composition provides highhardness and strength to enhance holding the hard particles 92 in themetal matrix 90. The eutectic composition also has good high temperatureproperties and retains strength at high temperatures rather thansoftening.

In one further example, the metal matrix 90 is, or predominantlyincludes, aluminum, and the hard particles 92 are, or predominantlyinclude, alumina (Al₂O₃). In an additional example, the hard particles92 are, or predominantly include, zirconia (ZrO₂). In yet anotherexample, the hard particles 92 are, or predominantly include, aluminaand zirconia. It is to be understood that the hard particles 92 are notlimited to alumina and zirconia, and other oxides, nitrides, carbides,oxycarbides, oxynitrides, diamond and combinations thereof can be usedselectively, with respect to heat-induced delamination of the polymericovercoat 62 a from frictional heat generated during rubbing between theabrasive tip 78 and the abradable seal 80.

The abrasive tip 78 can have a thickness in a thickness range of0.025-1.3 millimeters, and the hard particles 92 can have an averagemaximum dimension in a particle size range of 10-200 micrometers. Thehard particles 92 may protrude from the metal matrix 90 or be completelycovered by the metal matrix.

In one further example a polymer matrix filled with hollow glassmicrospheres for the abradable seal 80 is complimentary with a metalmatrix 90 of aluminum and hard particles 92 of alumina, zirconia, orboth in the abrasive tip 78, with respect to frictional heat generatedand heat-induced delamination of the polymeric overcoat 62 a. That is,the frictional heat generated between the abradable seal 80 and theabrasive tip 78 cause a blade 62 temperature at which the examplepolymer of the polymeric overcoat 62 a does not delaminate, or at leastmeets a delamination durability over an extended period of time, such asthe life of the engine 20.

In a further example, the abrasive tip 78 includes, by volume, 0.1-50%of the hard particles 92. For the above example based on use of apolymer matrix filled with hollow glass microspheres for the abradableseal 80 and a metal matrix 90 of aluminum and hard particles 92 ofalumina, zirconia, or both in the abrasive tip 78, an amount of 5-15% ofthe hard particles 92 can be used.

In the illustrated example in FIG. 4, the hard particles 92 are facetedand thus have angled facets 92 a. The angled facets 92 a providerelatively sharp corners that facilitate efficient “cutting” through theabradable seal 80 with low cutting forces, which lowers frictions and,in turn, contributes to lowering the amount of heat generated. In oneexample, the hard particles 92 are DURALUM ATZ II that haveapproximately 40% tetragonal zirconia with titania evenly distributedthroughout the individual alumina grains.

In another example shown in FIG. 5, an optional bonding agent 96 servesto facilitate bonding between the abrasive tip 78 and the metal-basedmaterial of the airfoil section 64. In one example, the bonding agent 96is a metallic bond coat that is located primarily between the abrasivetip 78 and the metal-based material of the airfoil section 64 and servesto enhance adhesion. For a metal matrix 90 of aluminum and a metal-basedmaterial of aluminum (of the airfoil section 64), the metallic bond coatcan be, or can predominantly include, nickel and aluminum. If galvaniceffects between dissimilar metals of the metallic bond coat and theabrasive tip 78 and/or airfoil portion 64 are of concern, the metallicbond coat can be excluded and a bonding agent 96 of an adhesive/sealantmaterial can be used instead to improve corrosion resistance in thepresence of moisture and also increase bonding strength.

The adhesive/sealant material can be a polymeric-based material, suchas, but not limited to, an epoxy or an epoxy-based material. Theadhesive/sealant material can infiltrate or partially infiltrate intopores of the abrasive tip 78 such that the abrasive tip 78, or at leasta portion thereof, and the underlying airfoil section 64 are protectedfrom corrosion. In a further example, the abrasive tip 78 can beprimarily directly bonded to the metal-based material of the airfoilsection 64, and the adhesive/sealant can fill or partially fill gaps orpores along the interface of the abrasive tip 78 and the underlyingairfoil section 64 to further enhance adhesion. In further examples, theadhesive/sealant could be, or could additionally be used as, anover-layer on top of the abrasive tip 78 to help close the tip gaps tothe abradable seal 80, such as for the shorter blades. On longer bladesthe adhesive/sealant may rapidly wear down until the abrasive tip 78starts cutting the abradable seal 80. In further examples, theadhesive/sealant can have an over-layer thickness of 0.0254-3.175millimeters, and in some examples a thickness of 0.254-1.27 millimeters.

The abrasive tip 78 can be a coating that is deposited onto the airfoilsection 64, or metallic bond coat 96, if used. For example, a thermalspray technique can be used, in which one or more feedstocks are fedinto a thermal plume. The feedstock can include individual powderfeedstocks of the metal of the metal matrix 90 and the hard particles92, or a single mixed feedstock powder of the metal of the metal matrix90 and the hard particles 92. In another alternative, the powderfeedstock can include composite particles of the metal of the metalmatrix 90 and the hard particles 92. Composite particles can include themetal and hard particles 92 in agglomeration or structured particlesthat have a hard particle 92 core and the metal overcoated around thecore. The hard particles 92 are not melted during the thermal spraydeposition. The deposition process can be controlled to avoid melting orsubstantial melting, to ensure that the hard particles 92 retain thefaceted geometry described above. It is desirable to retain as much ofthe faceted geometry as possible so that the cutting forces and heatgeneration are minimized during rub contact. In other alternatives, theabrasive tip 78 can be pre-fabricated and then attached to the airfoilsection 64, such as with an adhesive.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. A friction interface in a gas turbine engine,comprising: an abradable component and an abrasive component in rubbingcontact with each other, the abradable component being composed of apolymer matrix composite and the abrasive component being composed of ametal matrix and hard particles dispersed through the metal matrix, andthe metal matrix is an aluminum alloy and the hard particles areselected from the group consisting of oxides, nitrides, carbides,oxycarbides, oxynitrides, diamond and combinations thereof.
 2. Thefriction interface as recited in claim 1, wherein the aluminum alloy isa eutectic aluminum-silicon alloy.
 3. The friction interface as recitedin claim 1, wherein the hard particles have a particle size of 10micrometers to 200 micrometers.
 4. The friction interface as recited inclaim 1, wherein the hard particles protrude from the metal matrix. 5.The friction interface as recited in claim 1, wherein the abrasivecomponent has, by volume percent, 0.1% to 50% of the hard particles. 6.The friction interface as recited in claim 5, wherein the abrasivecomponent has 5% to 15% of the hard particles.
 7. The friction interfaceas recited in claim 1, wherein the polymer matrix composite includes asilica-containing filler.
 8. The friction interface as recited in claim7, wherein the silica-containing filler is hollow glass microspheres. 9.The friction interface as recited in claim 8, wherein the hard particlesinclude at least one of alumina or zirconia.
 10. The friction interfaceas recited in claim 9, wherein the abrasive component has, by volumepercent, 5% to 15% of the hard particles.
 11. The friction interface asrecited in claim 10, wherein the aluminum alloy is a eutecticaluminum-silicon alloy.
 12. A friction interface in a gas turbineengine, comprising: an abradable seal and an abrasive tip in rubbingcontact with each other, the abradable seal being composed of a polymermatrix composite and the abrasive tip being composed of a metal matrixand hard particles dispersed through the metal matrix, and the metalmatrix is aluminum alloy and the hard particles are selected from thegroup consisting of oxides, nitrides, carbides, oxycarbides,oxynitrides, diamond and combinations thereof.
 13. The frictioninterface as recited in claim 12, wherein the polymer matrix compositeincludes a silica-containing filler.
 14. The friction interface asrecited in claim 13, wherein the silica-containing filler is hollowglass microspheres.
 15. The friction interface as recited in claim 14,wherein the hard particles include at least one of alumina or zirconia.16. The friction interface as recited in claim 15, wherein the abrasivecomponent has, by volume percent, 5% to 15% of the hard particles. 17.The friction interface as recited in claim 16, wherein the aluminumalloy is a eutectic aluminum-silicon alloy.
 18. A blade comprising: anairfoil section extending between leading and trailing edges, first andsecond opposed sides each joining the leading and trailing edges, and aninner end and a free tip end, the airfoil section being formed of ametal-based material with a polymeric overcoat on at least one of theleading edge, trailing edge, first side and second side, the airfoilsection including an abrasive tip at the free tip end, the abrasive tipincluding a metal matrix and hard particles dispersed through the metalmatrix, and the metal matrix being composed of an aluminum alloy and thehard particles being selected from the group consisting of oxides,nitrides, carbides, oxycarbides, oxynitrides, diamond and combinationsthereof.
 19. The blade as recited in claim 18, wherein the polymermatrix composite includes hollow glass microspheres.
 20. The blade asrecited in claim 19, wherein the aluminum alloy is a eutecticaluminum-silicon alloy.